Lithium-ion batteries or lithium-ion battery systems have become established in practically all areas of mobile energy storage devices due to their high energy density and power density, regardless of whether they involve pedelecs, power tools, hybrid drives, electric vehicles, or even railway applications. At the same time, lithium-ion battery systems are becoming increasingly more important for stationery battery storage systems. A flat state of charge/voltage characteristic curve is characteristic of many lithium-ion cells or the cell chemistry thereof. In the marginal areas of less than about 10% and greater than 90% state of charge (SoC), the voltage level of the battery cells, however, changes very quickly. Over time, the battery cells can possibly drift apart from one another in their voltage level. This can occur through various effects such as, for example, various self-discharging rates, non-homogenous temperatures during operation, or even premature aging of a few cells in a battery system, or even due to different batches (supplied from different production batches).
In order to be able to evaluate the risk of a potential failure of a battery cell in advance, it is useful to detect or record state data from the ongoing operation of each battery cell and to document it for subsequent evaluation. This data includes, particularly, the temperatures of the cell that occur during operation, as well as the progression of charge and/or discharge currents and the corresponding states of charge. Storing data records at equal time intervals is known from the prior art. In the simplest case, this can be initiated through a clock generator, which initiates the storing of a data record at equal time intervals by creating a corresponding trigger signal. If a real time clock (RTC) is also available, the data record can also be equipped with a time-stamp or date-stamp. With storage at short time intervals, very large quantities of data can accrue. However, if the time interval between two storage processes is increased, this results in the risk that essential events will not be detected or recorded for evaluating a battery cell state.